This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The overall goal of this project is to develop an upper extremity robotic training system for use by people with stroke to practice arm and hand movement in the clinic or at home. The goal of the present study is to perform preliminary tests on a robotic orthosis that will assist, perturb, and measure naturalistic arm motion as part of the training system. The present study will test the robotic orthosis in a protected UCI environment. The orthosis is a modified version of the Wilmington Robotic Exoskeleton (WREX), which is a passive antigravity exoskeleton that uses rubber bands to make the arm feel weightless (Figure 1). WREX was originally designed by Dr. Tariq Rahman (Rahman et al. 1995) for use as an assistive device for children with muscular dystrophy. Children who are too weak to move their arm against gravity can self-feed and throw a ball, for example, by placing their arm in the orthosis. Previously the WREX design has been scaled by our laboratory for use as a movement training device to be used by adults with stroke (named "Training WREX" or "T-WREX"). The robotic orthosis used in this study is a pneumatically actuated version of T-WREX, called "Pneu-WREX".